General Science Mixed Quiz: Set 29

The correct answer is A, James Chadwick. Chadwick discovered the neutron in 1932 and won the Nobel Prize in Physics for it in 1935. He bombarded beryllium with alpha particles and found that the radiation given off was not affected by electric or magnetic fields, yet could knock protons out of paraffin. The only explanation was a particle with no charge and a mass close to that of the proton, which he named the neutron. It completed the picture of the atom, since the nucleus had earlier been short of mass, and it later made nuclear fission possible. Option B is wrong because Rutherford discovered the nucleus through his gold foil experiment and is credited with the proton. Option C is wrong because J. J. Thomson discovered the electron in 1897 with his cathode ray tube. Option D is wrong because John Dalton gave the atomic theory in 1803, long before subatomic particles were known. Exam tip: Thomson for the electron, Rutherford for the proton and nucleus, Chadwick for the neutron.

The correct answer is D, Ligament. A ligament is the connective tissue that joins one bone to another at a joint. It is very elastic and strong, and it holds the bones in place so that a joint can move without the bones slipping apart. Ligaments contain little matrix of their own and are stretched when a joint is twisted, which is what happens in a sprain. A is wrong because a tendon joins a muscle to a bone; tendons are fibrous and strong but have limited stretch, so the pull of a muscle is passed straight to the bone. B is wrong because cartilage is the smooth, flexible tissue that pads the ends of bones and shapes the nose and ear, cushioning the joint rather than tying the bones together. C is wrong because matrix is the material in which the cells of a connective tissue are embedded, not a structure by itself. Exam tip: ligament bone to bone, tendon muscle to bone.

The correct answer is A, 12 and 3. Benzene has the formula C6H6 and a ring of six carbon atoms, each carrying one hydrogen. Count the sigma bonds first: six carbon-carbon bonds around the ring and six carbon-hydrogen bonds give twelve sigma bonds. The ring also carries three carbon-carbon double bonds in the Kekule structure, and since every double bond is one sigma plus one pi, the extra component is three pi bonds. Option B is wrong because three counts only the pi bonds twice over and ignores the twelve sigma framework. Option C is wrong because six counts only the carbon-carbon sigma bonds and leaves out the six carbon-hydrogen bonds. Option D is wrong because nine is simply a distractor with no basis in the structure. The general rule to carry into the exam is that a single bond is one sigma, a double bond one sigma and one pi, and a triple bond one sigma and two pi.

The correct answer is B, tuberculosis (TB). The BCG vaccine takes its name from Albert Calmette and Camille Guerin, the two French scientists who developed it from a weakened strain of Mycobacterium bovis. In India it is given as a single dose soon after birth under the Universal Immunisation Programme, and it protects infants mainly from the severe forms of the disease, such as tuberculous meningitis and miliary tuberculosis. Tuberculosis itself is caused by the bacterium Mycobacterium tuberculosis, identified by Robert Koch in 1882, and it spreads through droplets when a patient coughs. Option A is wrong because typhoid, caused by Salmonella typhi, has its own conjugate vaccine. Option C is wrong because mumps is a viral disease covered by the MMR vaccine along with measles and rubella. Option D is wrong because plague, caused by Yersinia pestis and carried by rat fleas, needs a different vaccine. Exam tip: BCG at birth for TB, and World TB Day falls on 24 March.

The correct answer is D, blue. Borax, sodium tetraborate, is the salt of a strong base, sodium hydroxide, and a weak acid, boric acid, so its solution in water is basic. A basic solution turns litmus blue, which is the standard test. Option A is wrong because pink is the colour phenolphthalein takes in a base, not the colour of litmus; mixing up the two indicators is the usual mistake in this question. Option B is wrong because orange belongs to methyl orange, which is red in acid and yellow in base, and never gives a plain orange reading as an answer here. Option C is wrong because litmus turns red in an acidic solution, the opposite of what borax gives. Remember the pairing: salts of a strong base with a weak acid, such as borax, sodium carbonate and sodium acetate, all give a basic solution.

The correct answer is B, Rod-shaped. Bacteria are grouped by shape, and bacilli are the rod-shaped ones; the Latin word bacillus itself means a small rod or stick. Tuberculosis, tetanus, typhoid and anthrax are all caused by rod-shaped bacteria, and Lactobacillus, the bacterium that curdles milk into curd, belongs to the same group. The other shapes in this classification are cocci, which are spherical, spirilla, which are long and spiral, and vibrio, which are curved like a comma. A is wrong because comma-shaped bacteria are called vibrio, the best known being Vibrio cholerae, which causes cholera. C is wrong because spiral bacteria are spirilla and spirochaetes. D is wrong because spherical bacteria are cocci, such as Streptococcus. Exam tip: cocci are round, bacilli are rods, spirilla are spirals and vibrio are comma-shaped.

The correct answer is A, Cellulose and Pectin. Collenchyma cells lay down extra cellulose and pectin at the corners of their walls, which makes the tissue strong and yet flexible.

Collenchyma is a simple permanent tissue of plants, found just under the epidermis in the stems and leaf stalks of dicot plants and in the midrib of a leaf. Its cells are living and elongated, thickened unevenly at the corners, with almost no space between them. This uneven thickening lets a young shoot or a leaf stalk bend in the wind without breaking, and it is what allows climbing stems to twist.

Option B is wrong because lignin thickens sclerenchyma and cutin waterproofs the epidermis. Option C is wrong because chitin is found in fungal walls and insect skeletons, not in plant tissue. Option D is wrong because suberin is deposited in cork cells.

Exam tip: parenchyma has thin cellulose walls, collenchyma adds cellulose and pectin at the corners and stays flexible, sclerenchyma is lignified, dead and rigid.

The correct answer is B, Gamma rays. Gamma rays sit at the far end of the electromagnetic spectrum, with the shortest wavelength and therefore the highest frequency and energy. Arranged from the longest wave to the shortest, the spectrum runs radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All of them travel at the same speed in vacuum, so a shorter wave must have a higher frequency and each packet carries more energy. Gamma wavelengths are smaller than about 0.01 nanometre; they come out of the nucleus of a radioactive atom and are used to sterilise surgical instruments and to treat tumours. Option A is wrong because visible light measures roughly 400 to 700 nanometres, tens of thousands of times longer. Option C is wrong because infrared lies just beyond red and is longer than visible light, which is why we feel it as heat. Option D is wrong because X-rays are short but still longer than gamma rays, and they come from electrons, not the nucleus. Exam tip: the energy order is the reverse of the wavelength order.

The correct answer is B, Papaya. Papaya is raised from seed, so it is not multiplied by vegetative propagation the way the other three plants are.

Vegetative propagation means growing a new plant from a vegetative part of the parent, such as a stem, root, leaf or bud, without seeds. Because no seed is involved, the new plant is a copy of the parent and it also fruits sooner. Papaya has plenty of viable seed, and its soft unbranched stem does not strike roots from a cutting, so nurseries sow seed instead.

Option A is wrong because rose is the standard example of a plant grown from stem cuttings. Option C is wrong because banana is grown from suckers that come up from the underground stem, as its seeds are sterile. Option D is wrong because orange and other citrus plants are multiplied by budding and grafting on a rootstock.

Exam tip: cuttings give rose and sugarcane, suckers give banana, grafting and budding give citrus and mango, while papaya comes from seed.

The correct answer is B, Falciparum. Plasmodium falciparum causes malignant, or cerebral, malaria, the most dangerous form of the disease. Red blood cells infected by it become sticky and block the small blood vessels of the brain and other organs, which can lead to coma and death if treatment is delayed. Malaria spreads through the bite of the female Anopheles mosquito; the parasite first multiplies in the liver and then in red blood cells, and the bursting of these cells brings the cycles of chills and high fever. Ronald Ross proved the mosquito link in 1897 while working in India and won the Nobel Prize in 1902. Option A is wrong because P. vivax causes benign tertian malaria, which can relapse from dormant stages in the liver but is rarely fatal. Option C is wrong because P. ovale causes a mild tertian malaria found mainly in Africa. Option D is wrong because P. malariae causes quartan malaria, with fever every fourth day. Exam tip: falciparum = malignant; vivax = benign but relapsing; female Anopheles = vector.

The correct answer is C, Planimeter. A planimeter measures the area of any flat shape, however irregular its outline. The user simply traces the boundary of the shape on the map with the instrument's pointer, and a wheel and dial record the area swept, which is then multiplied by the square of the map scale. On a contour map this is how the area enclosed by a contour line, a catchment or a reservoir spread is worked out, so it is a standard tool in survey and irrigation work. A is wrong because areameter is not the accepted name of any such instrument. B is wrong because a clinometer measures the slope of ground or the angle of elevation of a point, not an area. D is wrong because a graphometer is an old surveying instrument used to measure horizontal and vertical angles. Exam tip: planimeter for area, clinometer for slope, planimeter plus contour map for catchment area.

The correct answer is D, Sickle cell anaemia, Haemophilia, Down syndrome. All three are genetic disorders, caused by changes in genes or chromosomes and passed on through birth, not by germs. Sickle cell anaemia is an autosomal recessive disease in which a single change in the haemoglobin gene makes red blood cells sickle-shaped. Haemophilia is a sex-linked recessive disorder carried on the X chromosome, in which blood does not clot properly; it mostly affects males, and it is called the royal disease because it spread among Queen Victoria's descendants. Down syndrome is a chromosomal disorder caused by an extra copy of chromosome 21, also called trisomy 21. Option A is wrong because AIDS is caused by the HIV virus and is not inherited through genes. Option B is wrong because AIDS and Hepatitis B are viral infections, and most cancers come from mutations acquired during life. Option C is wrong because Hepatitis B is a viral infection, even though haemophilia and colour blindness are genetic. Exam tip: genetic disorders include sickle cell anaemia, haemophilia, colour blindness, thalassaemia and Down syndrome.

The correct answer is A, strength of the intermolecular forces of attraction. Melting means breaking the particles free of the forces holding them in a fixed lattice, so a higher melting point means stronger forces of attraction. Heat supplied at the melting point does not raise the temperature at all; it is used as latent heat of fusion to overcome those attractions. This is why ionic solids such as common salt melt near 800 degrees Celsius while wax, held together by weak forces, melts in the warmth of a hand. Option B is wrong because repulsive forces act only when particles are pushed very close and they do not hold a solid together. Option C is wrong because molecular mass is a poor guide, as heavy iodine melts far below lighter silica. Option D is wrong because size matters only through the strength of the forces it creates, not on its own. Exam tip: stronger intermolecular forces mean a higher melting point and a higher boiling point together.

The correct answer is D, Galvanometer. A galvanometer detects whether a current is flowing in a circuit and shows its direction, because its needle moves to one side or the other about a central zero. It works on the turning effect of a magnetic field on a current carrying coil, and it is so sensitive that it responds to very small currents, which is why it is used to detect rather than to measure. The same instrument becomes an ammeter when a low resistance shunt is joined in parallel with it, and a voltmeter when a high resistance is joined in series. Option A is wrong because an ohmmeter measures resistance. Option B is wrong because a voltmeter measures potential difference and is connected in parallel across a component. Option C is wrong because a rheostat is a variable resistor used to change current, not to detect it. Exam tip: galvanometer detects, ammeter measures current in series, voltmeter measures voltage in parallel.

The correct answer is B, Cones. Cones are the photoreceptor cells of the retina that respond to colour in bright light. The human retina carries two kinds of photoreceptors. Cones number about six to seven million, sit densely near the centre of the retina and come in three types, sensitive to red, green and blue light; the brain mixes their signals into every shade we see. They work only when the light is good, which is why colours fade at dusk. Option A is wrong because rods are far more numerous but work in dim light and give only shades of grey, not colour. Option C is wrong because the blind spot is the point where the optic nerve leaves the eyeball and carries no photoreceptors at all. Option D is wrong because the fovea is a small pit in the retina, a place rather than a cell type, although it is packed with cones. Exam tip: rods for night and grey, cones for colour and daylight; colour blindness is a defect of the cones.

The correct answer is C, increases. Water behaves unlike most liquids between 0 and 4 degrees Celsius, a behaviour called the anomalous expansion of water. Almost every substance shrinks as it is cooled, but water shrinks only until it reaches 4 degrees Celsius. At that temperature it has its smallest volume and therefore its greatest density, about one gram per cubic centimetre. Cool it further, from 4 degrees down to 0 degrees, and it expands again, so one litre takes up more space at 0 degrees than at 4 degrees. This is why ice floats and why, in winter, a lake freezes only at the top while the water below stays at about 4 degrees, allowing fish to live through the cold. A and D are wrong because water only expands over this range, it does not shrink. B is wrong because the volume clearly changes. Exam tip: water is densest at 4 degrees Celsius.

The correct answer is C, a mechanism to reduce CO2 emission. A nuclear reactor splits heavy atoms; it burns no fuel, so it releases no carbon dioxide and needs no equipment to cut such emissions. The heat of fission is produced in the reactor core, carried away by a coolant, passed to water in a heat exchanger or steam generator, and the steam then turns a turbine coupled to a generator. Control rods of cadmium or boron absorb spare neutrons and a moderator such as heavy water slows them down so that fission continues steadily. Option A is wrong as a choice because the turbine is the part that actually converts steam energy into electricity. Option B is wrong because the heat exchanger carries heat from the radioactive coolant loop to the clean water loop. Option D is wrong because the reaction chamber, the core holding the fuel rods, is where fission happens. Exam tip: a nuclear plant emits no carbon dioxide; its waste problem is spent radioactive fuel instead.

The correct answer is C, 18% Tungsten. High-speed steel is named 18-4-1 after the three metals added to it in that order: 18 per cent tungsten, 4 per cent chromium and 1 per cent vanadium, with iron making up the rest along with a little carbon. Tungsten is the heart of the alloy because it keeps the steel hard even when the cutting edge glows red hot, so drills, milling cutters and lathe tools made from it can cut at high speed without losing their edge. Chromium adds hardness and resistance to rust, and vanadium refines the grain and improves wear resistance. A is wrong because chromium in this grade is 4 per cent, not 1. B is wrong because the 18-4-1 grade has no nickel; nickel goes into stainless steel and into invar. D is wrong because vanadium is the 1 per cent part of the name. Exam tip: 18-4-1 means tungsten 18, chromium 4, vanadium 1.

The correct answer is A, Used on ordinary combustibles such as wood and paper. Fires are sorted into classes by what is burning, and Class A covers ordinary solid fuels — wood, paper, cloth, straw, rubber and many plastics. These fires leave glowing embers, so they are put out mainly by cooling, and plain water or a water-based extinguisher is the cheapest and most effective choice for them. Option B is wrong because burning liquids such as petrol, kerosene, oil, paint and solvents are Class B, where water would spread the fire and foam or dry powder is used instead. Option C is wrong because a fire in live electrical equipment is a separate class — Class C in the American scheme and marked Class E in the Indian and European ones — and it needs a non-conducting agent such as carbon dioxide, never water. Option D is wrong because burning metals such as magnesium, sodium and potassium form Class D and need a special dry powder, since water reacts violently with them. Exam tip: A — solids, B — liquids, C — gases, D — metals, F or K — cooking oil.

The correct answer is A, Bryophytes. Bryophytes live on land but still need water to complete reproduction, so they are called the amphibians of the plant kingdom. Mosses, liverworts and hornworts belong here. They grow in damp, shady places, have no true roots, stems or leaves and no vascular tissue, so water moves through them by simple absorption. Their male gametes swim to the egg through a film of water, which ties them to moist ground exactly as frogs are tied to ponds. Option B is wrong because thallophytes are the algae, mostly water plants that never left water. Option C is wrong because pteridophytes, the ferns, are the first plants with true vascular tissue, xylem and phloem. Option D is wrong because gymnosperms such as pine and cycas bear naked seeds and use pollen, not swimming gametes. Exam tip: bryophytes are amphibians of the plant kingdom, pteridophytes are the first vascular plants, and gymnosperms are the first seed plants.